Split GCP-specific processors from general one (#42)

This introduces a new function to build the list of GCP-specific processors
and moves the non-GCP processors to the default processors builder.

This should allow people who want more configuration over the list of
processors (like more processors, or a different JSON renderer) to customize
their processors more easily, while still offering a default "go-to"
configuration function.

structlog_gcp/__init__.py

@@ -1,5 +1,6 @@
-from .base import build_processors  # noqa: F401
+from .base import build_gcp_processors, build_processors  # noqa: F401
 
 __all__ = [
+    "build_gcp_processors",
     "build_processors",
 ]

structlog_gcp/base.py

@@ -8,6 +8,44 @@ def build_processors(
     service: str | None = None,
     version: str | None = None,
 ) -> list[Processor]:
+    """Build structlog processors to export logs for Google Cloud Logging.
+
+    This builder function is expected to be your go-to function to expose structlog logs to Google
+    Cloud Logging format.
+
+    It configures the Google Cloud Logging-specific processors but also good defaults processors.
+
+    If you need more control over which processors are exactly configured, check the
+    :ref:`build_gcp_processors` function.
+    """
+
+    procs: list[Processor] = []
+
+    procs.extend(build_gcp_processors(service, version))
+    procs.append(structlog.processors.JSONRenderer())
+
+    return procs
+
+
+def build_gcp_processors(
+    service: str | None = None,
+    version: str | None = None,
+) -> list[Processor]:
+    """Build only the Google Cloud Logging-specific processors.
+
+    This builds a set of processors to format logs according to what Google Cloud Logging expects.
+
+    See: https://cloud.google.com/functions/docs/monitoring/logging#writing_structured_logs
+
+    Use this builder function if you want to customize the processors before and after the
+    GCP-specific processors.
+
+    In particular, this builder function **doesn't** configure the final JSON renderer. You are
+    expected to provide your own.
+
+    For a simpler, more general alternative, use :ref:`build_processors` instead.
+    """
+
     procs: list[Processor] = []
 
     # Add a timestamp in ISO 8601 format.
@@ -29,7 +67,4 @@ def build_processors(
     # Finally: Cloud Logging formatter
     procs.append(processors.finalize_cloud_logging)
 
-    # Format as JSON
-    procs.append(structlog.processors.JSONRenderer())
-
     return procs

tests/test_log.py

@@ -148,3 +148,19 @@ def test_extra_labels(stdout: T_stdout, logger: WrappedLogger) -> None:
         "test5": {"date": "datetime.date(2023, 1, 1)"},
     }
     assert msg == expected
+
+
+def test_core_processors_only(stdout: T_stdout, mock_logger_env: None) -> None:
+    processors = structlog_gcp.build_gcp_processors()
+    processors.append(structlog.processors.KeyValueRenderer())
+
+    structlog.configure(processors=processors)
+    logger = structlog.get_logger()
+
+    logger.info("test")
+    msg = stdout().strip()
+
+    # No JSON formmating, no contextvars
+    expected = "message='test' time='2023-04-01T08:00:00.000000Z' severity='INFO' logging.googleapis.com/sourceLocation={'file': '/app/test.py', 'line': '42', 'function': 'test:test123'}"
+
+    assert msg == expected